Coated steel sucker rods and process for manufacture of same

Abstract

In a process for applying a friction-resistant coating to a steel sucker rod, the rod is passed, in sequence, through a surface preparation stage (for example, scale removal, shot peening, or other suitable method), an adhesive application stage (to enhance the strength of the coating's bond to the rod), an extrusion stage (in which the rod is passed through a die in conjunction with a flow of melted polymeric coating material), and a cooling (coating solidification) stage. Typically, the radial thickness of the coating will be between 0.125 and 0.375 inches. The process is adaptable to apply extruded coatings to continuous rod or to individual sucker rods having upset ends. The coating may be selected from but is not limited to high-density polyethylene, cross-linked polyethylene, polyvinylidene fluoride, ethylene tetrafluoroethylene, polytetrafluoroethylene, polyphenylensulfide, nylon, polyester, polyethersulfone, polyethylene terephthalate, polypropylene, polystyrene, epoxy, or acetyl.

What is claimed is: 
     
       1. A process for applying a coating of a low-friction material to an elongate metal rod, said process comprising:
 preparing surfaces of the rod intended to receive the coating material by removing undesirable materials therefrom, using selected surface preparation means; 
 treating the prepared rod surfaces with a selected adhesive, wherein the metal rod is a steel rod having an upset threaded end, and wherein the adhesive treatment is not carried out with respect to the upset threaded end; 
 passing the adhesive-treated rod through an extrusion die of selected configuration without rotating the rod, while simultaneously flowing a melted low-friction material through the die, such that a coating of the low-friction material is deposited onto the adhesive-treated surfaces of the rod; and 
 using selected cooling means to solidify the coating of low-friction material. 
 
     
     
       2. A process as in  claim 1  wherein the coating of low-friction material has a radial thickness between 0.125 inches and 0.375 inches. 
     
     
       3. A process as in  claim 1  wherein the low-friction material comprises a polymeric material selected from the group consisting of high-density polyethylene, cross-linked polyethylene, polyvinylidene fluoride, ethylene tetrafluoroethylene, polytetra-fluoroethylene, polyphenylensulfide, nylon, polyester, polyethersulfone, polyethylene terephthalate, polypropylene, polystyrene, epoxy, or acetyl. 
     
     
       4. A process as in  claim 1  wherein the selected adhesive comprises an epoxy adhesive. 
     
     
       5. A process as in  claim 1  wherein the metal rod is a continuous steel rod. 
     
     
       6. A process as in  claim 1  further comprising applying a protective coating material to the upset threaded end of the rod prior to passing the rod through the extrusion die. 
     
     
       7. A process as in  claim 1  further comprising applying a protective coating material to the upset threaded end of the rod subsequent to passing the rod through the extrusion die. 
     
     
       8. A process as in  claim 6  wherein the protective coating is selected from the group consisting of epoxy coatings and baked-on powder coatings. 
     
     
       9. A process as in  claim 1  further comprising applying a bond-inhibiting agent to at least a portion of the upset threaded end of the rod prior to the step of passing the rod through the extrusion die. 
     
     
       10. A process as in  claim 1  wherein the metal rod is of generally round cross-section. 
     
     
       11. An elongate metal rod having a coating of a low-friction material, manufactured using a process as in  claim 1 , wherein the metal rod is a steel rod having an upset threaded end, and wherein the upset threaded end is not treated with adhesive. 
     
     
       12. A process for applying a coating of a low-friction material to continuous metal sucker rod, said process comprising:
 preparing surfaces of the rod intended to receive the coating material by removing undesirable materials therefrom using selected surface preparation means; 
 treating the prepared rod surfaces with a selected adhesive, the metal rod being a steel rod having an upset threaded end, and the adhesive treatment not being carried out with respect to the upset threaded end; 
 passing the adhesive-treated rod through an extrusion die of selected configuration without rotating the rod while simultaneously flowing a melted low-friction material through the die, such that a coating of the low-friction material is deposited onto the adhesive-treated surfaces of the rod; and 
 using selected cooling means to solidify the coating of low-friction material. 
 
     
     
       13. A process as in  claim 12  wherein the coating of low-friction material has a radial thickness between 0.125 inches and 0.375 inches. 
     
     
       14. A process as in  claim 12  wherein the low-friction material comprises a polymeric material selected from the group consisting of high-density polyethylene, cross-linked polyethylene, polyvinylidene fluoride, ethylene tetrafluoroethylene, polytetra-fluoroethylene, polyphenylensulfide, nylon, polyester, polyethersulfone, polyethylene terephthalate, polypropylene, polystyrene, epoxy, or acetyl. 
     
     
       15. A process as in  claim 12  wherein the selected adhesive comprises an epoxy adhesive. 
     
     
       16. A process as in  claim 12  wherein the continuous metal rod is a steel rod. 
     
     
       17. A process as in  claim 12  further comprising applying a protective coating material to the upset threaded end of the rod, prior to the step of passing the rod through the extrusion die. 
     
     
       18. A process as in  claim 12  further comprising applying a protective coating material to the upset threaded end of the rod subsequent to the step of passing the rod through the extrusion die. 
     
     
       19. A process as in  claim 17  wherein the protective coating is selected from the group consisting of epoxy coatings and baked-on powder coatings. 
     
     
       20. A process as in  claim 12  further comprising applying a bond-inhibiting agent to at least a portion of the upset threaded end of the rod prior to passing the rod through the extrusion die. 
     
     
       21. A process as in  claim 12  wherein the metal rod is of generally round cross-section. 
     
     
       22. A continuous metal sucker rod having a coating of a low-friction material, manufactured using a process as in  claim 12 , wherein the metal rod is a steel rod having an upset threaded end, and wherein the said upset threaded end is not treated with adhesive.